1. Field of the Invention
The present invention is related to wireless power transmission; more particularly, to an apparatus and method for detecting a foreign object in a wireless power transmitting system.
2. Description of the Related Art
In general, an external charger is used to charge portable terminals such as a mobile phone, notebook computer, or PDA by supplying electric energy or electric power thereto. Conventional portable terminals include battery cells storing supplied electric energy, and a circuit intended for charging and discharging the battery cells, thereby providing electric energy to the portable terminals.
The electrical interface between the charger and the battery cells, through which battery cells are charged with electric energy, may take the form of contacts. A contact-type electrical interface receives commercial electricity, transforms the electricity into voltage and currents relevant to the battery cells, and provides electric energy to the battery cells through the contacts of the corresponding battery cells.
Contacts of this kind require physical cables or use of electrical wires. Therefore, when a large number of terminals requiring the contact-type electric interface for energy are used, a large number of cables tend to occupy considerable workspace and may be unsightly or disorganized because it is not easy to arrange the cables properly. Moreover, the contact-type electrical interface may cause problems such as: instant discharge due to a potential difference between contacts, abrasion, risk of fire due to presence of flammable foreign objects, spontaneous discharge, decrease of battery lifetime, and degradation of battery performance.
Recently, to solve the aforementioned problems, charging systems employing wireless power transmission (hereinafter referred to as wireless power transmitting systems) and control methods for such systems have begun development. A wireless power transmitting method is also called a contactless power transmitting method or no point-of-contact power transmitting method. A wireless power transmitting system comprises a wireless power transmitting apparatus, which provides electric energy through wireless power transmission, and a wireless power receiving apparatus, which receives electric energy provided wirelessly from the wireless power transmitting apparatus and charges battery cells with the received electric energy.
Once connections are well secured between a charger and a mobile terminal, a contact-type electrical interface suffers little from obstacles disturbing battery charge, such as foreign objects. In contrast, because of the inherent characteristics of a wireless power transmitting system utilizing no-point-of-contact charge, there is a high chance that foreign objects could be inserted between the wireless power receiving apparatus and wireless power transmitting apparatus during charging. If a foreign object such as a metallic part is present between the wireless power receiving apparatus and wireless power transmitting apparatus, smooth power transmission is impaired due to the foreign object. Furthermore, problems such as damage and even detonation of the corresponding product due to overload and heating of the foreign object may result. Therefore, there is a need for an apparatus and method which detects foreign objects in a wireless power transmitting system.